1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to improvements in prosthetic feet.
2. Description of the Prior Art
The weight of a prosthetic foot is of paramount importance in prostheses. The foot is the component of the prosthesis that is furthest from the center of rotation ie., the knee joint.
The inertial resistance to changes of speed is directly proportional to the weight of any component but is proportional to the fourth power of the distance of any component from the center of rotation. Thus, the weight of the components that are farther away from the center of rotation is of much greater relevance than that of components that are closer to the center of rotation. For example, a reduction of one-tenth of a pound in the weight of a foot located fifteen (15) inches from a knee joint has the same effect on inertial resistance to changes in speed as a reduction of eight and one-tenths (8.1) pounds in the weight of a component five (5) inches from the knee joint.
What is needed, then, is a dynamic prosthetic foot having less weight than the dynamic prosthetic feet of the prior art.
Prosthetic feet have been made using carbon fibers in an epoxy matrix. Carbon-epoxy is a composite material with a very high strength to weight ratio, but not all sections of a prosthetic foot require the same flexural strength. Some sections are stressed much more than others. Moreover, not all sections of a prosthetic foot require the same rigidity. Some sections need to be more rigid than others and some sections need to be flexible.
Another need therefore exists for a prosthetic foot that is made with carbon reinforced composite that has a variable cross section density so that the sections thereof that require rigidity are rigid and the sections thereof requiring flexibility are flexible.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how to provide a dynamic prosthetic foot having variable cross section density.
The long-standing but heretofore unfulfilled need for an improved dynamic prosthetic foot is now met by a new, useful, and nonobvious dynamic prosthetic foot that is light-in-weight and that is made with a carbon reinforced composite having a variable cross section density.
The novel prosthetic foot includes a sole having an anterior, toe section and a posterior, heel section. An ankle part separates from the sole along a transverse parting line and includes a gradual upward bend and a vertically extending part.
A longitudinally extending slot divides the ankle part into a lateral pylon support and a medial pylon support. A lateral pylon connector is secured in trailing relation to the lateral pylon support and a medial pylon connector is secured in trailing relation to the medial pylon support.
The lateral pylon support has a greater thickness and thus less resiliency than the medial pylon support so that externally imparted forces appearing on the lateral pylon support are transferred at least in part to the medial pylon support whereby a sound leg may oppose the transferred forces.
A first convexity is formed in the sole and is adapted to perform a function like that of a ball of a natural foot. A second convexity is formed in the heel section, and said second convexity is adapted to perform a function like a bottom of a heel of a natural foot. A concavity is formed in the sole between the first and second concavities, and is adapted to perform a function like an arch of a natural foot.
In a second embodiment, the pylon connectors are eliminated and the lateral and medial pylon supports are elongated so that they become lateral and medial pylons, respectively. They are about twenty inches (20xe2x80x3) in length and are cut to length as required by a prosthetist when the novel foot is secured to a prosthetic socket.
The sole in the region of the first convexity is formed of a high strength outer layer made with carbon reinforced composite and an inner layer made of a matrix within which is dispersed a plurality of low density hollow spheres. The sole in the region of the concavity is formed of carbon-reinforced composite throughout.
An important object of this invention is to provide a prosthetic foot made with carbon reinforced composite having a variable cross section density.
A more specific object is to provide a prosthetic foot where the sections of the foot that are subjected to high stress, such as the ankle and the anterior section, are formed of carbon-reinforced composite throughout their entire cross section.
Another specific object is to provide a prosthetic foot where the sections of the foot that are not required to flex and that require high rigidity, such as part of the sole, the shin, and the upper part of the foot have a structure that includes a high strength outer layer made of carbon reinforced composite and an inner layer made in a matrix structure dispersed with low density hollow spheres such as carbon spheres or acrylonitrile spheres.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.